Cyanobacterial Heterocysts

Genomics of variation in nitrogen fixation activity in a population of the thermophilic cyanobacterium Mastigocladus laminosus

“…Average heterocyst frequency was 2.4 ± 0.3% (mean ± 95% confidence interval). This is lower than the~5-10% frequency typically reported for model heterocystous cyanobacteria (Kumar et al, 2010) but comparable to previous observations for M. laminosus (unpublished data). A significant correlation between heterocyst frequency and N fixation was only observed at 55°C (Pearson's correlation coefficient R = 0.50, Po0.01) but was positive in sign for all data sets (R = 0.17 and 0.30 for the 37°C and pooled data sets, respectively).…”

“…Strains were assayed at 37°C and 55°C, temperatures that delimit the approximate bounds of the population range. N fixation is energetically expensive, with high reductant requirements, and fixed carbon provisioned by adjacent vegetative cells contributes both electrons and a portion of the ATP budget for the process (Kumar et al, 2010). We therefore simultaneously estimated carbon fixation to test whether rates of N fixation and carbon fixation are correlated.…”

“…At White Creek, an N-limited, geothermally influenced stream in the Lower Geyser Basin of Yellowstone National Park, a population of the multicellular cyanobacterium Mastigocladus (Fischerella) laminosus fixes N by developing heterocysts (Miller et al, 2006), which are terminally differentiated cells that spatially separate the oxygen-sensitive N fixation process from photosynthetic oxygen produced by surrounding vegetative cells. N fixation has a complex genetic basis in heterocystous cyanobacteria (Kumar et al, 2010), requiring genes that regulate and specify the morphological and physiological changes that occur during the differentiation process, in addition to N fixation (nif) genes that are common to all diazotrophs. Estimates of the number of genes that are differentially regulated during heterocyst development range from~500 in Nostoc punctiforme (Campbell et al, 2007) to over 1000 in Anabaena PCC 7120 (Ehira et al, 2003).…”

Enhanced Resistance to UV-B Radiation in Anabaena sp. PCC 7120 (Cyanophyceae) by Repeated Exposure

“…PCC 7120. The strain was an ideal model for studying heterocyst differentiation when ammonium or nitrate is unavailable [19,30]. Mella-Herrera et al [38] found that conR was essential for heterocyst morphogenesis in Anabaena sp.…”

The pknH gene restrictively expressed in heterocysts is required for diazotrophic growth in the cyanobacterium Anabaena sp. strain PCC 7120

“…Heterocysts are terminally differentiated cells of filamentous cyanobacteria specialized for nitrogen fixation. Upon limitation of combined nitrogen in the medium, particular vegetative cells differentiate into heterocysts with a regular spacing of 10-15 cells (Flores & Herrero, 2010;Kumar et al, 2010). Heterocysts provide the microoxic environment for the oxygen-labile nitrogenase complex, the enzyme responsible for nitrogen fixation (Wolk et al, 1994).…”